The U.S. Navy's overarching strategy for defeating the Japanese by making a thrust through the Central Pacific had its roots in a long-standing concept for a maritime war with Japan. War Plan Orange dated to 1898, and though modified many times, the basic scheme remained consistent. Plan Orange called for marshaling the main battle fleet in the eastern Pacific, then steaming to the Philippines, where a decisive Mahanian-style battle fleet engagement would occur. Simultaneously, the navy would relieve the beleaguered Philippine army garrison. Faced with catastrophic defeat and total American command of the sea, Japan would presumably surrender.

The successful Japanese strike on Pearl Harbor completely disrupted Plan Orange and the Central Pacific thrust. With all Pacific Fleet battleships sunk or damaged and only five aircraft carriers available in the Pacific, the navy was in no condition to execute Plan Orange, defeat the Imperial Japanese Navy in a decisive battle for command of the sea, or even reinforce or evacuate the Philippine defenders. Consequently, for almost two years, the navy engaged in peripheral operations against the Japanese defensive perimeter, supporting the Marines and the army in the Solomon Islands and New Guinea and repelling Japanese main strike forces at the Battles of the Coral Sea and Midway.

By mid-1943, with Essex-class fleet carriers coming on line from the "two ocean" Naval Expansion Act of 1940 and fast battleships of the North Carolina–and South Dakota–classes for antiaircraft support and shore bombardment, the commander in chief of the Pacific Fleet, Admiral Chester Nimitz, stood ready to launch the Central Pacific assault against the Japanese Empire.

The dual-pronged Pacific strategy that emerged in 1943 represented a compromise between the services. The ABC Conference (between Britain, Canada, and the United States in March 1941) established Pacific operational areas, which the Joint Chiefs of Staff reconfirmed in March 1942. The agreement gave the navy operational control over the Central and South Pacific areas; the army had responsibility for the southwest Pacific. The army area commander, General Douglas MacArthur, advocated an advance up the New Guinea coast along the New Guinea–Mindanao axis to isolate the Japanese base at Rabaul and drive to the Philippines. The navy, meanwhile, pressed for a Central Pacific thrust. In March 1943, the Joint Chiefs agreed on a compromise plan whereby both services would advance along their preferred routes while simultaneously supporting each other. The results of this dual-pronged strategy formed from compromise were devastating for Imperial Japan.

To face two simultaneous threats, the Japanese, unable to concentrate against a single-threat axis, had to stretch their air, naval, and ground forces perilously thin. By adopting a "leap-frogging" operational mode in both the Central and southwest Pacific, U.S. forces could attack strategic points, such as islands with airfields, while simply bypassing and isolating large Japanese garrisons, such as Truk and Rabaul. These latter then withered on the vine.

Another component of the Central Pacific strategy was the submarine offensive against Japanese shipping. This offensive further reduced Japan's capability to reinforce and sustain isolated garrisons as U.S. forces advanced key island by key island, beginning with Operation galvanic against the Gilbert Islands in November 1943. In the interwar years, the Marine Corps had made great strides in amphibious operations, and Guadalcanal had been a useful test of amphibious doctrine. Nimitz and his chief of staff, Vice Admiral Raymond Spruance, had originally conceived of the first thrust going against the Marshall Islands; however, the Gilberts were closer to Hawaii and within range of land-based air cover.

The Central Pacific thrust offered a number of advantages. The many islands and atolls provided a target-rich environment that prevented the Japanese from determining the precise route of advance and forced them to defend all points. The size of the islands and atolls discouraged the establishment of large garrisons. The long distances between islands mitigated mutual support, and American carrier airpower inhibited supply and reinforcement. Further, the line of communications from Pearl Harbor and the mainland United States would be shorter than that to the southwest Pacific. The Central Pacific also offered a more healthful climate than the jungles of New Guinea. And an advance through the Central Pacific would cut off and isolate Japanese forces in the South Pacific.

There were, of course, some disadvantages to a Central Pacific thrust. These included the requirement for overwhelming naval and air superiority, which could not be achieved until late 1943 and necessitated the defeat of the main Japanese battle fleet (which occurred in the Battle of Midway). The U.S. plan would also rely on successful amphibious operations, which had not been totally proven.

Operation galvanic commenced in late autumn 1943 with landings on Tarawa Atoll (the primary objective being Betio, with its airfield) and Makin Atoll. The joint army, navy, and marine force employed overpowering numbers, with more than 200 ships and 35,000 troops under Rear Admiral Richmond K. Turner, commander of V Amphibious Force. Task Forces 52 and 53 assaulted the atolls on 20 November 1943. Six fleet carriers and five light carriers, escorted by six battleships, provided overwhelming firepower, naval gunfire support, and air cover. Additionally, several hundred army, navy, and marine aircraft participated from the base at Ellice Island. Despite Japanese air attacks from the Marshalls, the air threat proved negligible. On Tarawa, strong fortifications, bunkers, hidden obstacles, and barbed wire slowed the advance—a prelude to future Japanese defensive schemes—and with orders to fight to the last man, the garrison staunchly resisted. Very few Japanese survived, another indicator of the bitter struggle unfolding in the Central Pacific Campaign. U.S. forces suffered a 17 percent casualty rate and encountered other problems as well, including faulty beach and surf intelligence, the inability of landing craft to negotiate shallow atoll waters, inadequate landing craft, too little advance shore bombardment, and poor communications. The Gilberts experience provided many valuable lessons for the U.S. Navy and Marines on how to conduct future operations.

The Marshall Islands were next. Despite a dearth of transports, Operation flintlock finally commenced on 31 January 1944. Eniwetok and Kwajalein (the world's largest coral atoll) succumbed to overwhelming force and the pounding from Vice Admiral Marc Mitscher's Fast Carrier Task Force 58. The Americans had learned from the Gilberts experience, and casualties among the assaulting forces were much lighter. With the capture of the Marshalls by March, 10 weeks ahead of the established timetable, the navy bypassed several heavily fortified Japanese-held islands and turned its attention to the Mariana Archipelago.

The assault on the Marianas, Operation forager, aimed at taking Guam, Saipan, and Tinian Islands. From these bases, the Japanese home islands would be within striking distance of the B-29 Superfortress heavy bombers. The assault on Saipan commenced on 13 June 1944, with landings on 16 June. Determined to halt the advance by interdicting the supporting naval forces, Vice Admiral Ozawa Jisaburo mounted an assault on the Americans in the Battle of the Philippine Sea. However, the assault, which commenced on 19 June, turned into disaster as the better-trained and better-equipped U.S. Navy pilots decimated the inexperienced Japanese airmen in what came to be called the "great Marianas turkey shoot." Ozawa lost 325 of 375 attacking aircraft; Japanese naval airpower disappeared in a day, never to play any significant role in the war thereafter except in desperate suicide attacks in the last months.

Saipan was taken by 13 July. The Marines landed on Tinian on 24 July and secured it on 2 August. Guam, the last of the major islands, was struck on 21 July and was finally declared secured on 10 August.

With the loss of the Marianas, the Japanese defensive perimeter had been decisively breached. U.S. strategic bombing of the Japanese home islands now began in earnest and ended in the atomic bomb attacks launched from Tinian a year later. From the Marianas, the two prongs of the Pacific strategy came together again with the invasion of the Philippines in October 1944.

Tenacious Japanese defenders and their fortifications did cause heavy American casualties, and the difficulties inherent in staging such massive invasion efforts presented formidable challenges to U.S. operations. Nonetheless, the Central Pacific Campaign succeeded decisively. The Imperial Japanese Navy's hitherto deadly air arm had been utterly destroyed, and the stage was set for the final Allied thrust through the Philippines, Iwo Jima, and Okinawa and on toward the Japanese home islands.

Stanley D. M. Carpenter

Further Reading
Dull, Paul S. A Battle History of the Imperial Japanese Navy, 1941–45. Annapolis, MD: Naval Institute Press, 1978.; Harries, Meirion, and Susie Harries. Soldiers of the Sun: The Rise and Fall of the Imperial Japanese Army. New York: Random House, 1991.; Morison, Samuel Eliot. History of United States Naval Operations in World War II. Vol. 5, The Struggle for Guadalcanal, August 1942–February 1943. Boston: Little, Brown, 1949.; Spector, Ronald H. Eagle against the Sun: The American War with Japan. New York: Vintage Books, 1985.; Van de Vat, Dan. The Pacific Campaign: The U.S.-Japanese Naval War, 1941–1945. New York: Touchstone, 1991.